Lockheed Martin, the Pentagon's biggest IT and arms supplier, has thwarted a "significant and tenacious attack" on its computer network, it emerged yesterday.

In what appeared to be one of the most audacious acts of cyber-warfare conducted so far, the breach came against a backdrop of repeated attempts by rivals of the US, chiefly China and Russia, to infiltrate information networks and glean details of major weapons systems.

The company said that no customer or employee data had been compromised during the attack last week, while the Pentagon said the impact on its operations had been "minimal".

Yesterday however Lockheed was still working to restore employee access to its networks, and the experts from the Department Homeland Security and the Pentagon were trying to determine the extent of the data breach.

Lockheed is the maker of the F-16, F-22 and F-35 fighter jets as well as warships and other multibillion-dollar arms systems sold worldwide.

Officials had no information on the origin on the attack, but one of the US diplomatic cables released by the WikiLeaks website suggested that China had jumped ahead of the US when it came to cyber-espionage.